The semiconductor industry's tolerance for process variability continues to decrease as the size of semiconductor devices shrink. To meet these tighter process requirements, the industry has developed a host of new processes which meet the tighter process window requirements, but these processes often take a longer time to complete. For example, for forming layers conformally onto the surface of a high aspect ratio feature with a dimension of 65 nm or smaller, it may be necessary to use an ALD process. ALD is a variant of CVD that demonstrates superior step coverage compared to CVD. ALD is based upon atomic layer epitaxy (ALE) that was originally employed to fabricate electroluminescent displays. ALD employs chemisorption to deposit a saturated monolayer of reactive precursor molecules onto a substrate surface.
Film layers greater than one monolayer may be achieved by cyclically alternating the pulsing of appropriate reactive precursors into a deposition chamber. Each exposure of the deposition surface to a reactive precursor may be separated spatially and/or temporally by an inert gas purge and/or vacuum. The sequential exposure of a surface to the ALD precursor and reactant may add a new atomic layer to previously deposited layers to form a uniform material layer on the surface of a substrate. Cycles of reactive precursor(s) and inert purge gas(es) are repeated to form a material layer with a predetermined thickness.
Forming high-quality, stable dielectric layers of SiO2 has involved thermal reactions directly utilizing the silicon of the substrate, and CVD depositions utilizing various precursors, such as silane or dichlorosilane, and an oxygen source, for example N2O or O2, or reaction of tetraethyl orthosilicate (TEOS). These thermal and CVD depositions tend to require higher temperatures that are not necessarily suitable for depositions on substrates that have undergone previous processing, or have progressed to back-end-of-line (BEOL) processes. Films having smaller thicknesses are also difficult to produce by these methods.
In addition, few silicon related ALD precursors are stable at temperatures used for a high temperature (>650 C) deposition processes. The precursors tend to decompose at high temperature instead of forming a self-limited monolayer, resulting in poor film quality. Therefore, there is a need in the art for processes and precursors to form thin, high-quality, stable dielectric layers of SiO2 at temperatures below those typically utilized for thermal or CVD film growth yet having superior properties would therefore be advantageous.